It is well-known that when the fetal reserve is decreased, any diminution in maternal cardiac output, oxygenation of the maternal blood, or maternal uterine blood flow will place the fetus at significant subsequent risk for the development of fetal hypoxia and asphyxia (metabolic acidosis) if labor is allowed to continue. It is estimated that, in the United States, 700 infant deaths per year are the result of intrauterine hypoxia and birth asphyxia. It is also widely accepted that fetal neurological injury that develops during labor results from progressive hypoxia and acidemia severe enough to produce cerebral ischemia.
Electronic fetal monitoring (EFM) was introduced in the late 1950's in an attempt to permit timely intervention (e.g., expedited delivery by cesarean section) in situations in which the fetus appears to either be presently compromised already or will be so imminently. EFM has been widely adopted and is currently used in the majority of births in the United States.
EFM allows the early detection of fetal oxygen deprivation leading to hypoxia and metabolic acidosis through the reasonable interpretation of characteristic fetal heart rate (FHR) patterns. Generally speaking, however, the clinical interpretation of fetal heart monitor (FHM) data and interventions based on those interpretations have been quite inconsistent.
Traditionally, when any of the parameters of the FHM data demonstrate “reassurance,” labor is allowed to continue, with intervention being reserved for the situation when all of these parameters are abnormal, indicative of significant asphyxia (metabolic acidosis), or an acute emergency arises (e.g., fetal bradycardia). This approach, based on “rescue” of the fetus, has not resulted in improved outcomes either immediately or long-term. To date, there have been several publicized attempts at standardization of EFM interpretation, but deviations are commonplace and interpretation remains very subjective and with little physiological justification. Accordingly, there continues to exist a need for a more standardized interpretation of labor progress and FHR tracings, and which provides for the quantification of these parameters to objectively identify the level of risk for the subsequent development of adverse outcomes such as fetal hypoxia and acidosis if labor is allowed to continue without intervention.